Bibcode
Laporte, N.; Pelló, R.; Schaerer, D.; Richard, J.; Egami, E.; Kneib, J. P.; Le Borgne, J. F.; Maizy, A.; Boone, F.; Hudelot, P.; Mellier, Y.
Bibliographical reference
Astronomy and Astrophysics, Volume 531, id.A74, 17 pp.
Advertised on:
7
2011
Journal
Citations
20
Refereed citations
17
Description
Context. We investigate the nature and the physical properties of ten z,
Y, and J-dropout galaxies selected in the field of the lensing cluster
A2667. Aims: This cluster is part of our project aimed at
obtaining deep photometry at ~0.8-2.5 microns with ESO/VLT HAWK-I and
FORS2 on a representative sample of lensing clusters extracted from our
multi-wavelength combined surveys with Spitzer, HST, and Herschel. The
goal is to identify a sample of redshift z ~ 7-10 candidates accessible
to detailed spectroscopic studies. Methods: Our selection is
performed using the usual dropout technique based on deep I, z, Y, J, H,
and Ks-band images (AB ~ 26-27, 3σ), targeting z ≳ 7.5 galaxy
candidates. We also include IRAC data between 3.6 and 8 μm, and MIPS
24 μm when available. In this paper, we concentrate on the complete Y
and J-dropout sample among the sources detected with a high
signal-to-noise ratio in both H and Ks bands, as well as the bright
z-dropout sources fulfilling the color and magnitude selection criteria
adopted by Capak and collaborators. SED-fitting and photometric
redshifts were used to constrain the nature and the properties of these
candidates. Results: Ten photometric candidates are selected
within the ~7' × 7' HAWK-I field of view (~33 arcmin2
of effective area once corrected for contamination and lensing dilution
at z ~ 7-10). All of these are detected in H and Ks bands in addition to
J and/or IRAC 3.6 μm/4.5 μm images, with HAB ranging
from 23.4 to 25.2, and have modest magnification factors between 1.1 and
1.4. Although best-fit photometric redshifts are obtained at high-z for
all these candidates, the contamination by low-z interlopers is expected
to be in the range ~50-75% based on previous studies, and on comparison
with the blank-field WIRCAM Ultra-Deep Survey (WUDS). The same result is
obtained when photometric redshifts are computed using a luminosity
prior, allowing us to remove half of the original sample. Among the
remaining galaxies, two additional sources could be identified as low-z
interlopers based on a detection at 24 μm and the HST z850
band. These low-z interlopers are not accurately described by current
spectral templates given the large break, and cannot be easily
identified based on broad-band photometry in the optical and near-IR
domains alone. A good fit at z ~ 1.7-3 is obtained when assuming a young
stellar population together with a strong extinction. Given the
estimated dust extinction and high SFRs, some of them could also be
detected in the IR or sub-mm bands. Conclusions: After correction
for contaminants, the observed number counts at z ≳ 7.5 seem to
agree with expectations for an evolving LF, and be inconsistent with a
constant LF since z ~ 4. At least one and up to three candidates in this
sample are expected to be genuine high-z sources, although spectroscopy
is still needed to confirm this.
Based on observations collected at the European Southern Observatory,
Paranal, Chile, as part of the ESO 082.A-0163.